Geochemical Characteristics And Provenance Of Sandstone Of Dasheng Group Malanggou Formation In The Mid-part Of The Yishu Fault Zone,Shandong Province,China

The Yishu fault zone is the Shandong section of the Tan-Lu fault zone,dividing Shandong Province into two structural zonations:eastern and western Shandong.The Yishu fault zone is a main structural system in Shandong Province of eastern China,which plays an important role in controlling sedimentary formation and tremendous magmatic activities and mineralization in these regions.The sedimentary source,tectonic setting,and age of the Cretaceous Dasheng Group Malanggou Formation are of great significance for clarifying the relationship between the tectonic evolution and mineralization of the Yishu fault zone.In this paper,the malanggou formation of the middle part of the Yishu Fault Zone in the Dasheng Group of Cretaceous is taken as the research object.Based on the field survey,laboratory test and data analysis,the petrological characteristics,geochemical characteristics and provenance of the malanggou formation in the Dacheng Group are studied by using the knowledge of petrology,petrography and element geochemistry.Through the study of the petrological characteristics of sandstone in malanggou formation,it is found that the main rock type in the study area is felsic volcanic rock,which is seriously broken due to the influence of weathering and denudation.The petrographic characteristics show that the volcanic fragments are angular-subangular shape,and the psephicity of quartz is poor,which reflects the characteristics of proximal deposit.Analysis of the K2O/Na2O-SiO2 diagram and structural background discriminant map shows that the provenance area of Malangou Formation has a continental island arc structural background.Based on the analysis of the major elements of malanggou formation sandstone in Dasheng group,it is concluded that the provenance area of malanggou formation may suffer from weathering erosion.The analysis of chemical alteration index(CIA),composition variation index(ICV),Rb/Sr ratio,and Th/U-Th weathering degree discriminant graphs together shows that the provenance of malanggou formation in Dasheng group undergoes weak weathering and the maturity of sediment components is low.Based on the U-Pb dating of sandstone detrital zircons from the Malanggou formation of Dasheng group,it is found that the zircons of malanggou formation are mainly distributed in two ages:Mesozoic(117.7-141.7Ma)and Precambrian(1852-2499.4Ma),of which the proportion of Mesozoic zircons is higher.Combining with paleocurrent characteristics,it is inferred that zircons from the age of 117.7-141.7Ma originated from the western Shandong uplift,which is the main provenance;zircons from the age of 1852-2499.4Ma originated from the Yishui Group in the Gongdanshan uplift,which is the secondary provenance.In summary,Malanggou formation of Dasheng group is near source deposit,and there are two provenance areas,namely western Shandong uplift and Yishui Group in the Gongdanshan uplift;The provenance is formed in the continental island arc tectonic setting.The rock type is mainly volcanic volcanic rock,which is not strongly affected by weathering and erosion.